DETERMINATION OF THE VAPOR PRESSURE OF SODIUM


on the determination of the thermodynamic proper- ties of sodium, the variation of the vapor pressure with temperature was of interest. The normal boi...
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M. M. MAKANSI,C. H. MUENDEL AND W. A. SELKE

Vol. 59

DETERMINATION OF THE VAPOR PRESSURE OF SODIUM BY NI. M. MAKANSI,C. H. MUENDEL AND W. A. SELKE Departmmt of Chemical Engineering, Columbia Vniversiiy, New York, N . Y . Received July 19,1964

Experimental data on the vapor pressure of sodium in the pressure range 0.047 to 6.489 atm. have been obtained. The results are fitted by the equation log P = -5220/T 4.521, where P is in atm. and T is in degrees Kelvin,

+

Introduction In the work being conducted in this Laboratory on the determination of the thermodynamic properties of sodium, the variation of the vapor pressure with temperature was of interest. The normal boiling point of sodium was determined by Ruff and Johannsen in 1905l to be 877.5 f 5". Another determination of the boiling point by Heycock and Lamplough in 19122 gave a value of 882.9'. Previous workers had obtained data in the pressure range of 0.00049 to 760 mm. These data were reviewed by Ditchburn and Gilmour.J Rodebush and Walters4 obtained experimental data in the pressure range of 48.82 to 482.5 mm., and fitted them with the equation

- 5400

log P = T-

+ 4.6702

(1)

where P is in atm. and T in degrees Kelvin. Gordon5 and Kelleye using spectroscopic information on the dissociation of sodium dimer together with some vapor pressure data observed by other workers derived the following equations for the vapor pressure of sodium atoms and of sodium vapor, respectively. log log

P(Na)

=

P(Ns+Nan)

- 5702 -T

1.174 log T f.8.4437

- 5775 T -

1.274 log T

+ 8.863

(2)

(3)

According to Gordon, when equation 2 is corrected for the presence of sodium dimer molecules, it is accurate to 0.5%. Ditchburn and Gilmour3 correlating the experimental results of a number of workers, obtained the equation log P =

-5567 - 0.5 log 2' T

+ 6.354

(4)

According to them, the error in equation 4 is 5% in the range of 450 to 1200'I